In general, in a personal computer, a mobile communication device, and other personal information processing devices, an interface with a user is established using various input, devices, such as a keyboard, a mouse, or a digitizer. With the increasing development of mobile communication equipment, it is difficult to increase the degree of completion of products using only input devices, such as a keyboard and a mouse. Accordingly, there is an increased demand for a portable input device capable of achieving a simple structure and reducing erroneous operation. In order to meet such demand, a touch panel has been proposed in which the user directly touches the surface thereof with a hand (or a part thereof, such as a finger), a pen, or the like to input information.
This touch panel advantageously has a simple structure, less erroneous operation, character input capability without using other input devices, ease of transportation, and ease of user understanding. Accordingly, the touch panel is widely used in various information processing devices.
The touch panel is classified depending on the method of sensing a touch portion, and includes a resistive type in which a metal electrode is formed on an upper plate or a lower plate, and a touch position is determined depending on the voltage gradient based on resistance in a state where a DC voltage is applied to the metal electrode, a capacitive type in which the equipotential is formed in a conductive film and a touch positron is determined when a change in voltage of the upper or lower plate occurs due to a touch operation, an electromagnetic type in which the LC value induced when an electronic pen touches the conductive film is read to sense a touch position, and the like.
In one of the conventional methods of driving a touch panel, a method is known in which the touch panel is arranged on the display, and a change in an output signal is sensed in response to an input signal, such as current, to sense a touch position of a body part. This is called a mutual type or a mutual capacitance touch sensing type.
FIG. 1 shows a mutual type touch panel of the related art. The mutual type touch panel of the related art shown in FIG. 1 is configured such that separate bar-like driving layer 100 and sensing layer 200 are arranged perpendicular to each other, as shown in FIG. 2. Further, an insulating layer 102 is interposed between the driving layer 100 and sensing layer 200, as shown in FIG. 3.
In the mutual type touch panel configured as shown in FIG. 3, when a body part, such as a finger, touches the upper part of the touch panel, a change in mutual capacitance between the sensing layer 200 and the driving layer 100 is measured to sense the presence/absence of a touch operation.
At this time, as shown in FIG. 4, an undesired capacitance (e.g., parasitic capacitance) CH is formed between a body part 400, such as the finger of a person who touches the protective film 402 (e.g., glass) at the upper part of the touch panel and the sensing layer 200. The parasitic capacitance value affects the value of mutual capacitance CM for measuring the presence/absence of a touch operation. Accordingly, it is necessary to change the pattern of the sensing layer 200 to reduce or minimize parasitic capacitance.
To this end, in the related art, as shown in FIG. 5, there is an attempt to decrease the width 500 of the sensing layer, thereby reducing parasitic capacitance between the body part, such as the finger which touches the protective film, and the sensing layer.
As shown in FIG. 5, when the width of the sensing layer decreases, parasitic capacitance between the sensing layer and the body part, such as the finger, also decreases, causing a decreased parasitic capacitance component to be measured. However, there is a problem in that a resistance component increases, causing a decrease in a current or voltage resulting from mutual capacitance.
If the width of the sensing layer 200 is excessively small, as shown in FIG. 5, the minimum area between the sensing layers for recognizing the body part expands, making it difficult to recognize an object having a small area during a touch operation.